A. Field of the Invention
The present invention relates to methods and apparatus for measuring pressures exerted on the feet of standing humans or animals such as horses. More particularly, the invention relates to a method and apparatus for providing a two-dimensional map of pressures exerted on the bottom of a human foot by a shoe, for example, or on the hoof of an animal, particularly, a horse.
B. Description of Background Art
People who must be on their feet for long periods of time, whether standing or walking, are well aware of the discomfort and fatigue that may be brought on by reaction pressures exerted on the bottoms of the feet by the ground or other surface supporting the weight of the person. Accordingly, substantial efforts have been exerted by manufacturers of shoes, ski boots and other footwear, in an effort to more uniformly distribute the pressures exerted by footwear on the feet of the wearer. In conjunction with these efforts, a variety of devices for measuring the forces applied to the foot by footwear have been disclosed in the following United States patents:
Levin et al., U.S. Pat. No. 4,121,453, Oct. 24, 1978, Foot Force Transducer, which discloses an apparatus for measuring foot forces during walking that uses a specially configured spring seated in a transducer plate to transmit static and dynamic forces on the foot during walking to strain gauges mounted on the transducer plate, which in turn, may be monitored and recorded for diagnostic purposes, particularly to aid in treating patients with lower extremities dysfunction.
Confer, U.S. Pat. No. 4,745,930, May 24, 1988, Force Sensing Insole For Electro-Goniometer, which discloses a force sensing insole that is adapted to be used in association with an electro-goniometer for analyzing the gait of a patient. The insole includes a body member composed of three overlying sheets of thin plastic material which are bonded together, with the intermediate sheet having cut-outs in each of the heel, ball and tow portions so as to define three separate internal chambers. A contact switch is positioned in each of the open chambers, and which comprises a plurality of parallel fingers formed of conductive ink on the inwardly facing surface of one of the outer sheets, and an area of conductive material on the inwardly facing surface of the outer sheet. The body member includes a laterally extending flexible strip, and which is adapted to flex and extend outwardly from the wearer's shoe. Also, lines of conductive ink are provided in the body member which extend from each of the contact switches to a terminal positioned at the end of the strip. In the preferred embodiment, switch closures are input to a radio frequency transmitter strapped to the waist of a subject, a remote receiver being used to monitor switch closures.
Franks, U.S. Pat. No. 4,858,621, Aug. 22, 1989, Foot Pressure Measurement System, which discloses a foot pressure measurement system in which pressure measurements are obtained from the variation of light output from an illuminated glass or transparent plate. A reflective material on the top surface of the plate causes an increase in light intensity escaping from the plate when pressure is applied to the reflective material. The accuracy and resolution of the pressure measurements are improved by obtaining a reference measurement of the background light intensity and distribution before pressure is applied and subsequently subtracting this background light from the light patterns produced when pressure is applied. The reflectance characteristics of the system are improved by using a photographic paper as the reflective material.
Seitz, U.S. Pat. No. 4,862,743, Sep. 5, 1989, Device For Measuring The Areal Distribution of Compressive Forces, which discloses a device for measuring the areal distribution of compressive forces which act substantially vertically with respect to a deformable measuring surface. A matrix arrangement of force sensors is provided, each of which is formed as a capacitance at crossings of substantially perpendicular conductor paths. The conductor paths are fixed on the opposed surfaces of an elastically deformable area-type dielectric and adapted to be connected by conductive elements to evaluator electronics. The conductor paths are printed on plastic substrate films.
Podoloff et al., U.S. Pat. No. 5,033,291, Jul. 23, 1991, Flexible Tactile Sensor For Measuring Foot Pressure Distributions And For Gaskets, which discloses a force and pressure sensor having two sets of parallel electrodes which are positioned facing one another and arranged so that electrodes of one set cross the electrodes of the second set at an angle to create a plurality of electrode intersections. Pressure-sensitive resistive material lies between the electrodes at each intersection. An adhesive layer is applied to at least one of the electrode sets in areas between electrode intersections to secure the first and second electrode sets in facing relationship, the adhesive layer preferably being applied in a pattern which provides passages where the adhesive layer does not exist to allow air to escape from interior areas of the electrode set. The thickness of the adhesive layer may be adjusted to permit preloading or to provide a threshold level for the sensor. In order to permit electrodes of the electrode set to be trimmed around their periphery, electrical contact to each electrode of the electrode sets is made intermediate the ends of the electrodes. This is accomplished by providing an insulating layer over the rear of each electrode set having holes therein at the desired intersection points and having a plurality of connecting conductors on the back of the insulating sheet, one for each electrode, which make contact with the corresponding electrode through the hole in the insulating sheet.
Fullen et al., U.S. Pat. No. 5,323,650, Jun. 28, 1994, System For Continuously Measuring Forces Applied To The Foot, which discloses a self-contained system for measuring forces applied to the foot of a user that includes a force sensor array positioned within the user's shoe between the foot and the inner sole of the shoe, the force sensor array including a multiplicity of individual force sensors arranged in a hexagonal pattern that covers the entire area of contact between the sole of the user's foot and the inner sole of the shoe, an electronic circuit module removably attached to the side of the shoe, and a flat interconnecting cable for electrically coupling the force sensor array to the electronic circuit module. The electronic circuit module includes a central processing unit, read-only memory, random access memory, and scanning circuitry for electronically continuously scanning the force sensor array to obtain information indicative of an instantaneous force sensed by each one of the multiplicity of individual force sensors of the force sensor array, for processing that information to obtain force data, and for storing the force data in the random access memory. An annunciator audibly signals the user when a force on the foot greater than a predetermined threshold force is sensed.
In addition to the aforementioned references, the following United States patents disclose devices generally adapted to the measurement of pressures exerted on body parts:
Bourland et al., U.S. Pat. No. 5,010,772, Apr. 30, 1991, Pressure Mapping System With Capacitive Measuring Pad, which discloses a capacitive measuring pad for measuring the pressures exerted by various portions of a patient's body on a mattress. The pad is constructed of transverse conductive strips separated by a compressible insulator to form a matrix of pressure sensitive capacitive nodes. The nodes are repetitively scanned in sequence by a microcomputer to measure their respective capacitances, from which measurements a pressure map is then derived. The resulting pressure map may be displayed on a color graphics monitor with different colors representing different pressures. Node capacitance is found by measuring the response of the node to a driving signal of a known voltage. This measurement is accomplished by connecting one of the node's transverse conductive strips to a sense amplifier. In order to isolate the node of interest from the influence of surrounding nodes, all of the conductive strips except the two intersecting the selected node are connected to ground. Furthermore, the input impedance to ground of the sense amplifier is made negligibly small with respect to the other system impedance. In this way, only the conductive strip connected to the driving source has a voltage impressed on it, and the conductive strips of all other nodes in the system are maintained at ground potential, thus allowing an accurate measurement of the one capacitance.
Tamori, U.S. Pat. No. 5,079,949, Jan. 14, 1992, Surface Pressure Distribution Detecting Element, which discloses a detecting element for sensing surface pressure distributions comprising a substantially rigid insulating substrate, a plurality of scanning row electrodes, formed by metal deposition on said substrate, etched to form a pattern of substantially parallel electrodes which are spaced apart and oriented along a first axis, a thin resistive film, deposited on said substrate, having a resistance which varies as a function of contact area, a substantially resilient deformable surface layer, a plurality of scanning column electrodes, formed by metal deposition on said surface layer, etched to form a pattern of substantially parallel column electrodes which are spaced apart, said surface layer being bonded to said substrate by an anisotropic adhesive so that said column electrodes are oriented along a second axis which is perpendicular to said first axis, said surface layer transmitting pressure distribution to said row electrodes, resistive film, and column electrodes to form a matrix of variable contact resistances to provide analog information relating to the distribution of surface pressure applied to said surface layer.
Rincoe et al., U.S. Pat. No. 5,253,656, Oct. 19, 1993, Apparatus And Method For Monitoring Contact Pressure Between Body Parts And Contact Surfaces, which discloses an apparatus and method for monitoring pressure between the surface of a body part and a contact surface employing a plurality of pressure sensors disposed in a matrix array between the contact surface and the body part. The sensors produce analog force signals proportional to pressure, and a monitor receives the analog signals and produces output signals, preferably digital, having pressure data corresponding to the pressure at each sensor. A computer processor receives the output signals from the monitor to create a force profile for the sensor array. The sensors may be scanned as a read event in variety of manners, including periodic continuous and triggered scanning. Where triggered scanning is desired, one or more switches act to initiate a read event. This monitoring apparatus and method is used, for example, to fit prosthetics, to monitor bed-ridden and wheelchair-bound patients, to reduce paid and sores caused by uneven distribution of pressure and to monitor pressure between a cast and a person. The sensors may be mounted on a single sheet or on strips for positioning along the body, and monitoring is accomplished by multiplexing and digitizing the analog force signals.
In addition to the references cited above, the present inventor disclosed in U.S. patent application Ser. No. 08/254,918, filed Jun. 6, 1994, novel Multi-Directional Piezoresistive Shear And Normal Force Sensors For Hospital Mattresses And Seat Cushions. Although the sensors disclosed in the aforementioned application are an important advancement in the field, the required characteristics of foot pressure sensors are somewhat different from those for hospital mattresses and seat cushions.
In addition to the problem of accurately mapping pressures exerted on human feet, a need exists for performing such measurements on the hooves of animals, particularly horses. Since the substantial weight of a horse is concentrated on relatively small portions of the horse's hooves, it should be the goal of the farrier who fits horseshoes to hooves to trim the hoof in a manner causing the weight of the horse to be distributed relatively uniformly over both those portions of the hoof in contact with the shoes, and those portions in contact with the ground. The present inventor is unaware of any prior art devices that are intended for, or particularly well adapted to, mapping pressures exerted on the hooves of an animal.